The Berkeley Pit, a former open pit copper mine in Butte, Montana, is approximately 1 mile long and 1/2 mile wide. When mining operations ceased, all dewatering activities also ceased. Consequently, the pit continues to fill with groundwater. The water in the pit is acidic and contains high concentrations of certain pollutants, including iron, copper, zinc, sulfates and arsenic.

This picture was taken from the visitor's viewing platform in July 2009.